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Investigation of multi-ion heat and neoclassical transport using new edge main ion measurements at ASDEX Upgrade.

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Title: Investigation of multi-ion heat and neoclassical transport using new edge main ion measurements at ASDEX Upgrade.
Authors: Cano-Megias, P.1,2 (AUTHOR) pcano1@us.es, Viezzer, E.2 (AUTHOR), McDermott, R.M.1 (AUTHOR), Angioni, C.1 (AUTHOR), Fable, E.1 (AUTHOR), Jansen van Vuuren, A.3 (AUTHOR), Cavedon, M.4 (AUTHOR), Cruz-Zabala, D.J.2 (AUTHOR), Dux, R.1 (AUTHOR), Manas, P.5 (AUTHOR), P.-Gonzalez, J.2 (AUTHOR), Takacs, R.1 (AUTHOR), Zimmermann, C.F.B.1,6 (AUTHOR), Chacartegui, R.2 (AUTHOR)
Source: Nuclear Fusion. Sep2025, Vol. 65 Issue 9, p1-22. 22p.
Subjects: H-mode plasma confinement, Deuterium ions, Velocity, Plasma boundary layers, Thermal conductivity, Tokamaks, Heat transfer, Transport theory
Abstract: This study provides new insights into multi-ion heat transport and the validation of neoclassical theory at the edge of H-mode plasmas. Utilizing a high-resolution main ion charge exchange recombination spectroscopy system, the first characterization of edge deuterium temperature (TD) and toroidal velocity ( v ϕ , D ) in a metal wall environment is presented. Dedicated experiments which examine the impact of the heating mix on TD and v ϕ , D in the ASDEX Upgrade tokamak are discussed. An unexpected temperature difference between main ions (TD) and impurities (Tz) was discovered when increasing P ECRH , T D > T z . The new temperature measurements have been used to solve the multi-ion heat transport equations with the astra transport code. The interpreted deuterium (χ D ) and impurity (χ z ) heat diffusivities have been compared to fluid (tglf) and gyrokinetic (gkw) models. While the dependence of a qualitatively similar χ D / χ z on the ion to electron heat flux ( Q i / Q e ) was identified in both experiment and simulation, discrepancies in the absolute value between the two are found when temperature differences between deuterium and impurities are present. The mechanism for the χ D / χ z dependence on Q i / Q e is the stronger resonant interaction of impurities with low drift frequency turbulence modes in comparison to deuterium. Importantly, it is shown that considering a single ion species (i), and assuming T D = T z gives reasonable estimates of χ D ≈ χ i for the cases studied here. On the contrary, the evaluation of χ z is very sensitive to ion temperature differences, which must be considered for accurate impurity ion heat transport description. Additionally, differences between v ϕ , D and v ϕ , z were compared to neoclassical calculations. Neoclassical theory can accurately describe v ϕ , D (provided an independent measurement of v ϕ , z or Er) in the steep gradient region, but not at the pedestal top nor bottom, highlighting the complexity of edge transport phenomena. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:This study provides new insights into multi-ion heat transport and the validation of neoclassical theory at the edge of H-mode plasmas. Utilizing a high-resolution main ion charge exchange recombination spectroscopy system, the first characterization of edge deuterium temperature (TD) and toroidal velocity ( v ϕ , D ) in a metal wall environment is presented. Dedicated experiments which examine the impact of the heating mix on TD and v ϕ , D in the ASDEX Upgrade tokamak are discussed. An unexpected temperature difference between main ions (TD) and impurities (Tz) was discovered when increasing P ECRH , T D > T z . The new temperature measurements have been used to solve the multi-ion heat transport equations with the astra transport code. The interpreted deuterium (χ D ) and impurity (χ z ) heat diffusivities have been compared to fluid (tglf) and gyrokinetic (gkw) models. While the dependence of a qualitatively similar χ D / χ z on the ion to electron heat flux ( Q i / Q e ) was identified in both experiment and simulation, discrepancies in the absolute value between the two are found when temperature differences between deuterium and impurities are present. The mechanism for the χ D / χ z dependence on Q i / Q e is the stronger resonant interaction of impurities with low drift frequency turbulence modes in comparison to deuterium. Importantly, it is shown that considering a single ion species (i), and assuming T D = T z gives reasonable estimates of χ D ≈ χ i for the cases studied here. On the contrary, the evaluation of χ z is very sensitive to ion temperature differences, which must be considered for accurate impurity ion heat transport description. Additionally, differences between v ϕ , D and v ϕ , z were compared to neoclassical calculations. Neoclassical theory can accurately describe v ϕ , D (provided an independent measurement of v ϕ , z or Er) in the steep gradient region, but not at the pedestal top nor bottom, highlighting the complexity of edge transport phenomena. [ABSTRACT FROM AUTHOR]
ISSN:00295515
DOI:10.1088/1741-4326/adf3cb